1. Field of the Invention
The present invention relates to centrifugal pumps and particularly to centrifugal pumps effective for pumping slurries of liquid, usually water, and suspended solids constituting up to about 25 percent by weight of such slurries. Usually, the slurries have chunks or lumps of solid material that could clog or otherwise reduce the efficiency of a centrifugal pump so that such slurry pumps must have mechanism for comminuting the lumps or chunks to ensure effective and consistent pumping of the slurry.
2. Prior Art
The pump of the present invention is of the same general type as the "Centrifigual Chopping Slurry Pump" disclosed in U.S. Pat. No. 3,973,866 which is stated to be an improvement on the general type of pump disclosed in U.S. Pat. No. 3,155,046. The pumps of both of those patents are designed for pumping slurries containing chunks or lumps of solid material.
In general, each of the prior pumps has an upright drive shaft, the lower end portion of which projects downward into a substantially cylindrical pump casing. The impeller fixed to the drive shaft within the casing has a radial shroud disc or plate with downward projecting, generally radially extending blades or vanes. The bottom of the casing is closed by an end plate having arcuate inlet apertures for intake of slurry in an axial direction. The sharpened lower edges of the impeller blades cooperate with the leading edges of the inlet apertures for chopping chunks or lumps of solid material in the slurry being pumped. The slurry is accelerated circumferentially and outward to a generally tangential outlet conduit.
The pump disclosed in U.S. Pat. No. 3,973,866 also includes a screw propeller cantilevered from the pump drive shaft outside the pump casing and adjacent to the inlet apertures in the end plate. Such propeller has generally radial blades with somewhat sharpened leading edges for chopping chunks or lumps in the slurry. In addition, the screw propeller is stated to generate a positive current flow of slurry through the end plate inlet apertures.
Another aspect of the pump of U.S. Pat. No. 3,973,866 that is pertinent to the present invention is the use of elongated "slinger" ribs or vanes of small axial height projecting from the side of the impeller shroud plate opposite the lower primary pumping impeller blades. Such upper vanes are in the form of volute ribs for slinging away from the drive shaft bearing structure the solid material component of slurry which may work its way past the edge of the shroud plate so as to reduce wear of such bearing structure. See the paragraph beginning at column 2, line 21.
The prior pumps are of relatively low head and efficiency as compared to the pump of the present invention. In such pumps flow through the end plate inlet apertures into the impeller-receiving pump casing and out of the casing through the pump outlet is much more turbulent than in the pump of the present invention.